A gas turbine engine generally includes, in serial flow order, a compressor section, a combustion section, a turbine section and an exhaust section. In operation, air enters an inlet of the compressor section where one or more axial compressors progressively compress the air until it reaches the combustion section. Fuel is mixed with the compressed air and burned within the combustion section to provide combustion gases. The combustion gases are routed from the combustion section through a hot gas path defined within the turbine section and then exhausted from the turbine section via the exhaust section.
In particular configurations, the turbine section includes, in serial flow order, a high pressure (HP) turbine and a low pressure (LP) turbine. The HP turbine and the LP turbine each include various rotatable turbine components such as turbine rotor blades, rotor disks and retainers, and various stationary turbine components such as stator vanes or nozzles, turbine shrouds and engine frames. The rotatable and the stationary turbine components at least partially define the hot gas path through the turbine section. As the combustion gases flow through the hot gas path, thermal energy is transferred from the combustion gases to the rotatable turbine components and the stationary turbine components.
Nozzles utilized in gas turbine engines, and in particular HP turbine nozzles, are often arranged as an array of airfoil-shaped vanes extending between annular inner and outer bands which define the primary flowpath through the nozzles. Due to operating temperatures within the gas turbine engine, it is generally desirable to utilize materials having a low coefficient of thermal expansion and high compression strength. Recently, for example, ceramic matrix composite (“CMC”) materials have been utilized to operate effectively in such adverse temperature and pressure conditions. These low-coefficient-of-thermal-expansion materials have higher temperature capability than similar metallic parts, so that, when operating at the higher operating temperatures, the engine is able to operate at a higher engine efficiency.
However, CMC materials have mechanical properties that must be considered during the design and application of the CMC. For example, CMC materials have relatively low tensile ductility or low strain to failure when compared to metallic materials.
Typical vanes are held within the turbine engine using radial pins disposed through a vane band or engine support. During operation, these pins can create high tangential loads and stress concentrations for the nozzle and associated attachment features. In addition, existing pins can create high tensile loads that may be especially harmful to CMC materials. Therefore, if a CMC component is restrained using certain pin structures, stress concentrations can develop leading to a shortened life of the segment.
To date, nozzles formed of CMC materials have experienced localized stresses that have exceeded the capabilities of the CMC material, leading to a shortened life of the nozzle. The stresses have been found to be due to moment stresses imparted to the nozzle and associated attachment features, differential thermal growth between parts of differing material types, and loading in concentrated paths at the interface between the nozzle and the associated attachment features.
Accordingly, improved nozzles and nozzle assemblies are desired in the art.